Everybody's making a big hoopla over this week's guest mentor. Why? Because he and Simon Cowell haven't exactly seen eye to eye in the past. In fact, both were quite open in their disdain for each other. Here's another hint - tonight's theme is disco. Yes, Will Young has been helping the remaining acts warble their way through disco hits for the past week. Is anyone else picturing Daniel in a tight white suit a la Saturday Night Fever? Dermot O'Leary presents the fourth live studio round, which sees the nine remaining acts performing disco songs. As well as impressing the public, they will be keen to sway judges and mentors Cheryl Cole, Simon Cowell, Dannii Minogue and Louis Walsh, who will decide the fate of the two acts with the fewest votes. The results can be seen at 9.50pm - where Will Young performs his new single. Ah, be nice - he wrote this one himself.